Crowther's stage experience began in the mid-1940s. As a youngster he showed promise as a pianist, and in 1944 won a junior scholarship to the Royal Academy of Music. He attended the respected Cone-Ripman Drama School in London, where he met his future wife, and whilst there competed (in 1947) at the Star Junior Ballroom Championships partnering Pamela Cochran, and then at 16, he appeared as a member of the Ovaltineys Concert Party of the Air on Radio Luxembourg. He also attended Nottingham High School and then Thames Valley Grammar School.

In November 1951 his mother died of a massive stroke aged 56.[citation needed] His father, Leslie Frederick Crowther, was also an actor.[citation needed] Leslie senior was an alcoholic, and died in early January 1955 at the age of 67, ten days after being hit by a car.[citation needed] Leslie junior had a half-brother, Frank Ronald, from his father's first marriage.[citation needed]

During the late 1950s and early 1960s, Crowther worked on the stage and on radio. His radio work included Ovaltine programmes, Variety Playhouse and Crowther's Crowd.

Crowther made a name for himself in television in the 1950s, with appearances as presenter of such programmes as the Billy Cotton Band Show and The Black and White Minstrel Show, and later the long-running children's institution Crackerjack (with Peter Glaze) for the BBC, from 1960 to 1968. In September 1967, Crowther was the presenter chosen to host the first series of the revamped children's favourites show, Junior Choice, on the newly opened Radio One station. The next year, 1968, he recorded the LP 'Songs for Swinging Children', released on Pye's blue Label.

From 1964 to 1967, Crowther presented Meet the Kids, an annual trip to a children's hospital ward that was screened by the BBC on Christmas Morning. He would walk around the ward meeting the patients, and the show would feature a surprise celebrity, and a present hidden under each bed. Typical locations were Great Ormond Street or Hackney Hospitals. In 1969, Crowther switched to ITV, and A Merry Morning was screened annually, following the same format, usually from the Seacroft Hospital in Leeds.[4]

Mid-1977 Crowther made an effort to break into radio with the pilot of a comedy show, ''It's Leslie, by Crowther'', recorded in the Regent Sound Stage (now the Vue Cinema in Lower Regent Street) and produced by John Browell. This however did not come to anything and he returned to TV.

Crowther was one of the many hosts of the ITV panel/game show Whose Baby? which he presented in the mid-1980s. He also presented the fifth series of Southern Television's children's game show Runaround in 1977, standing in for Mike Reid. He was also host of the first British version of the game show The Price is Right, from 1984 to 1988, during which time his "Come on down!" catchphrase became familiar. In 1994, Crowther said that when The Price is Right was axed in May 1988, the producers never bothered to contact him directly. Instead, he learned the news from the press who called at his house and asked him how he felt.

In February 1990, he was chosen to be host of the TV show Stars in Their Eyes. The first episode was transmitted on 21 July 1990. Crowther hosted the first three series, and a Christmas special in 1991. At the time of his car crash in October 1992 he was booked to record an Elvis Presley special, hosted by Russ Abbot, and a fourth series, eventually hosted by Matthew Kelly.

Crowther's show business career came to a sudden end on the afternoon of 3 October 1992 on the M5 near Cheltenham, when he sustained serious head injuries in a car crash which nearly killed him. The precise cause is unknown. It was speculated that he fell asleep at the wheel and, as a result, his Rolls-Royce car skidded into the central reservation barrier and overturned several times. In the months before the crash, Crowther was extremely busy with Lord's Taverners events and functions and on the previous day, 2 October, had been to a dinner in Swansea. That night he stayed at a hotel in Birmingham, and then opened some Allied Carpets stores in Birmingham on the morning of 3 October. Crowther was returning home when the crash occurred.[5]

The car ended up on its roof on the hard shoulder of the motorway, and was a write-off. At first Crowther did not appear to be seriously injured, apart from being shaken up and sustaining a cracked bone in his neck. He was able to tell the police his personal details, including his home telephone number and what tablets he was taking for his heart condition; he had been diagnosed with heart trouble three years earlier when he complained of feeling breathless.

In his autobiography, he claimed the stress of the media harassment over his alcoholism in late 1988 and early 1989 had brought it on. However, after being taken to Cheltenham General Hospital, his condition suddenly deteriorated and he lapsed into unconsciousness. A brain scan revealed a blood clot had formed on the left-hand side of his brain. Crowther was taken to Bristol's Frenchay Hospital for brain surgery to remove the blood clot that evening.

On 5 October, after a nurse was unhappy with his condition, a further scan revealed that another blood clot, the size of a small apple, had formed on the same side of his brain. Crowther then underwent a second brain operation that lasted two hours and a tracheotomy to help him breathe. Crowther remained in a coma for 17 days. He came home for the first time just before Christmas 1992. He was a patient in Frenchay Hospital until 12 February 1993 when he was discharged. After his release, he underwent months of occupational therapy and physiotherapy.[6]

Crowther was appointed a CBE in the 1993[7]New Year's Honours list in recognition of his years of charity work and in July 1993 he went to Buckingham Palace to receive it. On 20 November 1993, he made his first TV appearance since his crash in the Royal Variety Performance, appearing alongside Cilla Black. On stage, he announced that he had just started to write an autobiography. Entitled The Bonus of Laughter, it was published in the autumn of 1994. On 6 October 1994, he and Matthew Kelly were interviewed together on This Morning.

Crowther retired from show business on 4 November 1994, accepting that "I wouldn't be able to do things I've done the way I would want to, and the way my fans would expect". He also said that he was considering starting a new career as a writer. As he later put it, his mind was still sharp but his body had slowed down. Five days after retiring he appeared as the subject on This Is Your Life for the second time, when he was surprised by Michael Aspel during a book-signing session in Selfridges on London's Oxford Street. He had previously been honoured by This Is Your Life in March 1973 when Eamonn Andrews surprised him at an antiques fair at Earls Court in London. Two weeks after the second This Is Your Life tribute, Crowther appeared on the BBC's Invitation to Remember, in which he looked back on and reminisced about his career. Crowther's final television appearance was in March 1995, as a guest on June Whitfield's This Is Your Life episode.

Like his father, Crowther was an alcoholic and this problem continued throughout the 1960s, 1970s and 1980s. On 14 November 1983, Crowther was arrested for drink-driving. Two weeks later he was fined, and banned from driving for nine months. This did not deter Crowther and in October 1988, he turned up at a gala in Glastonbury, drunk. This made him realise that he had a serious problem and needed help. Unlike five years earlier, his alcohol addiction received much publicity. From January to 17 March 1989, Crowther was a resident in Clouds House, a drug and alcohol treatment centre near Shaftesbury. He never drank alcohol again.

Crowther married Jean Elizabeth Stone (12 May 1931 - 10 December 2017) on 27 March 1954. They had five children, including twins born on 9 December 1954; one of the twins, his daughter, Liz, is an actress. Another daughter, Caroline, was married to the musician Phil Lynott. Crowther's youngest child, Nick, works in radio, presenting traffic and travel bulletins for AA Roadwatch based in Stanmore.[8]

The 30 September 1996 episode of Bruce's Price Is Right, the Bruce Forsyth version of The Price is Right, was dedicated to Crowther at the request of Forsyth himself, according to the ITV continuity announcement. Forsyth told the Daily Mirror the previous day that Crowther had written to congratulate him on obtaining the job of presenting The Price is Right when it was relaunched on 4 September 1995.

Crowther was cremated a week later, on 7 October. His ashes were later scattered at Lord's and a memorial service was held for him in London on 27 November. Also in October, at that year's National Television Awards, Matthew Kelly dedicated an award he won for Stars In Their Eyes to Crowther.